Broadband Photoresponsive Bismuth Halide Hybrid Semiconductors Built with π-Stacked Photoactive Polycyclic Viologen

Photoresponse ranges of commercially prevailing photoelectric semiconductors, typically Si and InGaAs, are far from fully covering the whole solar spectrum (similar to 295-2500 nm), resulting in insufficient solar energy conversion or narrow wave bands for photoelectric detection. Recent studies have shown that infinite pi-aggregation of viologen radicals can provide semiconductors with a photoelectric response range covering the solar spectrum. However, controlled assembly of an infinite pi-aggregate is still a great challenge in material design. Through directional self-assembly of electron-transfer photoactive polycyclic ligands, two crystalline inorganic-organic hybrid photochromic viologen-based bismuth halide semiconductors, ((Me)(3)pytpy)[BiCl6]center dot 2H(2)O [1; (Me)(3)pytpy = N,N',N ''-trimethyl-2,4,6-tris(4-pyridyl)pyridine] and ((Me)(3)pytpy)[Bi2Cl9]center dot H2O (2), have been synthesized. They represent the first series of pytpy-based photochromic compounds. After photoinduced coloration, the conductivities of both 1 and 2 increased. The radical products have electron absorption bands in the range of 200-1600 nm, exceeding that of Si. Both the conductivity and the photocurrent intensity of 2 are stronger than those of 1, due to better planarity, tighter pi-stacking, and higher degrees of overlap of ((Me)(3)pytpy)(3+) cations. This study not only provides a new design idea for synthesizing radical-based multispectral photoelectric semiconductors but also enriches the family of electron-transfer photochromic compounds.

Automated summary

This study demonstrated the synthesis of two crystalline inorganic-organic hybrid photochromic viologen-based bismuth halide semiconductors, representing a new series of pytpy-based photochromic compounds. The radical products showed electron absorption bands in the range of 200-1600 nm, exceeding that of Si. The conductivity and photocurrent intensity of the semiconductors were influenced by factors such as planarity, pi-stacking, and cation overlap.